That is about 59.6% relative humidity. Switch to dew point mode to go the other way, from a hygrometer reading to the dew point.
How the dew point calculator works
DewPointCalc uses the Magnus formula with the Alduchov and Eskridge constants a = 17.625 and b = 243.04 °C. With the air temperature T in °C and relative humidity RH, it computes γ = ln(RH/100) + a·T/(b + T), and the dew point is b·γ/(a − γ). Going the other way, RH = 100·exp(a·Td/(b + Td) − a·T/(b + T)). Absolute humidity comes from the saturation vapour pressure, 6.112·exp(17.67·T/(T + 243.5)) hPa, times RH × 2.1674 divided by the temperature in kelvin. A surface at or below the dew point gets condensation; for painting, keep it at least 5 °F (3 °C) above.
Dew point comfort chart
| Dew point | Feels | Notes |
|---|---|---|
| Below 40 °F (4 °C) | Very dry | dry skin and static are likely, especially indoors |
| 40–54 °F | Comfortable | pleasant for most people |
| 55–59 °F | Slightly humid | still comfortable for most, a little sticky for some |
| 60–64 °F | Humid | sticky; most people notice the moisture |
| 65–69 °F | Muggy | uncomfortable, sweat evaporates slowly |
| 70–74 °F | Oppressive | very uncomfortable; take care with exercise |
| 75 °F (24 °C) and up | Miserable | dangerous for strenuous activity |
Dew point at 70 °F by humidity
| Relative humidity | Dew point |
|---|---|
| 20% | 27.1 °F |
| 30% | 37.1 °F |
| 40% | 44.6 °F |
| 50% | 50.5 °F |
| 60% | 55.5 °F |
| 70% | 59.8 °F |
| 80% | 63.5 °F |
| 90% | 66.9 °F |
Frequently asked questions
How do I calculate relative humidity?
RH = 100 × exp(a·Td/(b+Td) − a·T/(b+T)) with a = 17.625 and b = 243.04 °C, the Magnus approximation.
Why does humidity drop in the afternoon?
The moisture stays about the same while the air warms, and warm air can hold more, so the relative humidity falls.
What indoor humidity is best?
About 30–50% for comfort and to limit mould and dust mites.
Is DewPointCalc free?
Yes, with no sign-up or ads, and your readings stay in your browser.
How accurate is the result?
The formula is accurate to about 0.4 °C; most home hygrometers are only accurate to 2–5% RH, which matters more.